Core wire for guide wire and method for manufacturing the same

ABSTRACT

Provided is a core wire for guide wire in which high rigidity can be attained even with a fine wire diameter so that pushability is improved while the core wire is prevented from fatigue deformation, and a method for manufacturing the core wire. 
     This core wire  15  for guide wire is made of a Ti—Ni based alloy and has a wire diameter not larger than 0.5 mm and a Young&#39;s modulus not lower than 50 GPa. According to the manufacturing method, first, wire drawing is performed on a raw material M 0  so that the raw material M 0  is passed through a wire drawing dice  2  to be drawn to a certain length while the wire diameter of the core wire is reduced. Thus, a primary processed material M 1  is formed. After that, the primary processed material M 1  is hammered and drawn by swaging dices  5  and  5  so that a secondary processed material M 2  is formed. In this manner, the core wire  15  having a wire diameter not larger than 0.5 mm and a Young&#39;s modulus not lower than 50 GPa is manufactured.

TECHNICAL FIELD

The present invention relates to a core wire for guide wire which servesas a material of a guide wire for use in introduction of a catheteretc., and a method for manufacturing the core wire.

BACKGROUND ART

In the background art, contrast media or medical agents are dosedthrough a catheter for inspection or treatment in a tubular organ suchas a blood vessel or a trachea. The catheter is inserted to an intendedplace through a narrow and soft guide wire. For radiography or treatmentin a coronary artery, a cerebral artery or another narrow tubular organwhose diameter is reduced due to disease, a microscopic catheter is usedand a microscopic guide wire is also used correspondingly.

The guide wire is required to have properties such as pushability withwhich a pushing force on the operating side can be transmitted to afront end portion of the guide wire or torque transmissioncharacteristic with which a blood vessel can be selected in a bifurcatedvessel.

Stainless steel, Ti—Ni based alloy, etc. may be used as the material ofsuch a guide wire.

The stainless steel is hard and has high rigidity. Therefore, anarrow-diameter guide wire formed of the stainless steel is superior inpushability. However, since the stainless steel is brought into fatiguedeformation easily, the original performance and function of thestainless steel guide wire is apt to be spoiled in the course of use.

On the other hand, the Ti—Ni based alloy is superior in flexibility soas to be prevented from fatigue deformation. However, since the Ti—Nibased alloy is softer and lower in rigidity than stainless steel, themicroscopic guide wire formed of the Ti—Ni based alloy is apt to beinsufficient in pushability, torque transmission characteristic, etc.Thus, there have been some proposals for guide wires made of Ti—Ni basedalloys with enhanced rigidity.

For example, Patent Document 1 discloses a catheter guide wire includinga core material and a coating portion applied on the surface of the corematerial, wherein the core material is formed of a Ti—Ni based alloycontaining 45 to 52 at % Ni, and at least one of an exothermic amountand an endothermic amount of the Ti—Ni based alloy caused by martensitictransformation and martensitic reverse transformation is not higher than0.80 cal/g.

Patent Document 2 discloses catheter guide wire including a Ti—Ni alloycore wire and an outer circumferential member applied on the core wirefrom outside, wherein a sectional area of a front end portion of thecore wire is smaller than that of any other portion of the core wire bya chemical process and/or a mechanical process. An example of theaforementioned mechanical process is swaging or rolling.

Patent Document 3 discloses a method for manufacturing a catheter guidewire in which a sectional area of a front end portion of a Ti—Ni alloycore wire having superelasticity in a temperature range of from 0° C. to40° C. is made smaller than that of any other portion of the core wireby at least one process selected from a group consisting of etchingprocessing, cutting/grinding and swaging, and the core wire obtainedthus is coated with an outer circumferential member from outside.

PRIOR TECHNICAL DOCUMENTS Patent Documents

Patent Document 1: JP-H05-293175-A

Patent Document 2: JP-H06-165822-A

Patent Document 3: JP-H11-128363-A

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

Since the guide wire of Patent Document 1 has a Young's modulus of about40 GPa as shown in its test example, sufficient rigidity to be used formicroscopic blood vessel may not be obtained.

In Patent Document 2, the front end portion of the core wire in theguide wire is processed to be narrower than any other portion of thecore wire by a chemical process and/or a mechanical process. When thefront end portion of the core wire is processed by a mechanical process,the rigidity of the front end portion of the core wire is enhanced bywork hardening. However, an intermediate portion and a base end portionof the core wire are not processed at all but remain soft. The rigidityof the core wire as a whole is not enhanced. Thus, a pushing forceacting at the base end portion of the core wire cannot be transmitted tothe front end portion efficiently, and there is a problem in terms ofpushability.

Also in Patent Document 3, only the front end portion of the core wireis processed by cutting, swaging etc. The rigidity in the intermediateportion and the base end portion of the core wire cannot be enhanced,and there is a problem in terms of pushability as in Patent Document 2.

An object of the present invention is to provide a core wire for guidewire in which high rigidity can be attained even with a fine wirediameter so that pushability is improved while the core wire isprevented from fatigue deformation, and a method for manufacturing thecore wire.

Means for Solving the Problems

A first invention provides a core wire for guide wire, wherein the corewire is made of a Ti—Ni based alloy, has a wire diameter not larger than0.5 mm and has a Young's modulus not lower than 50 GPa.

According to the above invention, the core wire has high rigidity to benot lower than 50 GPa in Young's modulus while the core wire has thefine wire diameter not larger than 0.5 mm. Thus, the core wire has highpushability which is required when the core wire is inserted into atubular organ, and the core wire is prevented from fatigue deformation.Accordingly, the core wire can be used suitably for guide wire, forexample, to be inserted into a narrow blood vessel of a heart, a brain,etc.

A second invention provides, based on the first invention, the corewire, wherein wire drawing and swaging are performed on the core wire.

According to the above invention, the two processes of wire drawing andswaging are performed so that the working degree of the core wire isimproved. Thus, high rigidity can be attained in spite of the fine wirediameter.

A third invention provides, based on the first or second invention, thecore wire, wherein the Ti—Ni based alloy is a work-hardened Ti—Ni basedalloy whose texture has a microcrystalline structure.

In the case where either the wire drawing or the swaging alone isperformed alone, the texture has a structure close to an amorphousstructure. When both the wire drawing and the swaging are performed asin the core wire, the texture has a microcrystalline structure. As aresult, prevention from fatigue deformation can be attained even in theprocessed state of the core wire while the mechanical characteristicsare improved to keep the rigidity. Thus, the core wire can be usedsuitably for microscopic guide wire.

A fourth invention provides, based on the second or third invention, thecore wire, wherein heat treatment as well as the wire drawing and theswaging is performed on the core wire.

According to the above invention, the heat treatment is performed sothat strain or residual stress caused by the wire drawing and theswaging can be relaxed. Thus, the linearity which is essential as a corewire for guide wire can be enhanced while the rigidity is attained.

A fifth invention provides, based on any one of the first to fourthinventions, a method for manufacturing the core wire including: drawinga raw material made of a Ti—Ni based alloy, and then carrying outswaging to obtain a core wire having a wire diameter not larger than 0.5mm and a Young's modulus not lower than 50 GPa.

According to the above invention, the two processes of wire drawing andswaging are performed. Thus, a core wire which has high rigidity to benot lower than 50 GPa in Young's modulus and which is prevented fromfatigue deformation can be obtained.

A sixth invention provides, based on the fifth invention, the methodfurther including: performing heat treatment after the swaging.

According to the above invention, strain or residual stress caused bythe wire drawing and the swaging can be eliminated by the heattreatment. Thus, it is possible to obtain a core wire which has rigidityand is prevented from fatigue deformation and which has high linearity.

Effect of the Invention

According to the invention, the core wire has high rigidity to be notlower than 50 GPa in Young's modulus while the core wire has a fine wirediameter not larger than 0.5 mm. Thus, the core wire has highpushability and is prevented from fatigue deformation, and the core wirecan be used suitably for guide wire to be inserted into a narrow bloodvessel of a heart, a brain, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is sectional view showing an embodiment of a core wire for guidewire according to the invention.

FIGS. 2A to 2C illustrate a method for manufacturing the guide wireaccording to the invention, FIG. 2A illustrating a state before wiredrawing, FIG. 2B illustrating a state where the wire drawing is beingperformed, FIG. 2C illustrating a state where swaging is beingperformed.

FIG. 3 is a stress-strain diagram of Comparative Examples 1 to 3 forexamining influence of heat treatment on materials subjected to wiredrawing.

FIG. 4 is a stress-strain diagram of Comparative Examples 4 to 6 forexamining influence of heat treatment on materials subjected to swaging.

FIG. 5 is a stress-strain diagram of Comparative Example land Examples 1to 3 for examining influence of heat treatment on materials subjected toboth wire drawing and swaging.

FIG. 6 is a stress-strain diagram of Comparative Example 7 and Examples4 and 5 for examining influence of kind of swaging on materialssubjected to wire drawing.

FIGS. 7A and 7B show an observed texture of Example 1 by a transmissionelectron microscope, FIG. 7A being a photograph of the texture, FIG. 7Bbeing an electron diffraction pattern.

FIGS. 8A and 8B show an observed texture of Example 1 by thetransmission electron microscope at a different place from that in FIGS.7A and 7B, FIG. 8A being a photograph of the texture, FIG. 8B being anelectron diffraction pattern.

FIGS. 9A and 9B show an observed texture of Comparative Example 1 by thetransmission electron microscope, FIG. 9A being a photograph of thetexture, FIG. 9B being an electron diffraction pattern.

FIGS. 10A and 10B show an observed texture of Comparative Example 4 bythe transmission electron microscope, FIG. 10A being a photograph of thetexture, FIG. 10B being an electron diffraction pattern.

FIG. 11 is a graph showing results of Vickers hardness tests onComparative Examples 1 and 4 and Example 1.

MODE FOR CARRYING OUT THE INVENTION

An embodiment of a core wire for guide wire according to the inventionwill be described below with reference to the drawings.

This core wire for guide wire (hereinafter referred to as “core wire”)is used so as to be disposed in an internal center of a guide wire. Forexample, the core wire can be applied to a guide wire 10 shown inFIG. 1. The guide wire 10 in this embodiment includes a core wire 15according to the invention and a resin layer 17 applied on an outercircumference of the core wire 15. A front end portion of the core wire15 is tapered off with a diameter gradually reduced toward the tip.

The core wire in this embodiment is made of a Ti—Ni based alloysubjected to wire drawing and swaging. The core wire is formed to have awire diameter not larger than 0.5 mm and a Young's modulus not lowerthan 50 GPa.

A Ti—Ni based alloy which is good in biocompatibility and suitable for aguide wire, such as Ti—Ni, Ti—Ni—Cu, Ti—Ni—Fe, Ti—Ni—Nb, etc., is usedas the material of the core wire. In addition, alloy elements such as V,Cr, Mn, Co, etc. may be added to the Ti—Ni based alloy (each of thealloy elements has a role of reducing transformation temperature).

The core wire made of the aforementioned Ti—Ni based alloy is furthersubjected to wire drawing and swaging. In the “wire drawing”, a rawmaterial is drawn out through a dice with a certain hole shape or theraw material is inserted into the hole of the dice and extrudedtherefrom, thereby processing the raw material into a wire with acertain shape. In the “swaging”, an outer circumference of the rawmaterial is hammered and drawn using a rotating dice, thereby processingthe raw material into a desired shape.

A working ratio P₁ when the raw material is drawn is preferably notlower than 10%, more preferably not lower than 20%, and the mostpreferably not lower than 30%. When the working ratio P₁ is lower than10%, the work hardening of the raw material is insufficient so that therawmaterial cannot have satisfactory rigidity. The working ratio P₁mentioned herein can be derived from the following Expression (i), inwhich A₀ designates a sectional area of the raw material and A₁designates a sectional area of the raw material (primary processedmaterial) subjected to wire drawing. Although it is preferable that theworking ratio is higher, a contrivance for processing may be necessarywhen the working ratio is higher than 60%.

Working Ratio P ₁(%)={(A ₀ −A ₁)/A ₀}×100   (i)

The processing order is not limited as long as the core wire issubjected to both the wire drawing and the swaging, but it is preferablethat after wire drawing (primary process) is performed on the rawmaterial, swaging (secondary process) is performed on the raw material(primary processed material) subjected to the wire drawing. In thiscase, a working ratio P₂ when the primary processed material is swagedis preferably not lower than 5%. Further, a total working ratio (P₁+P₂)of this working ratio P₂ and the aforementioned working ratio P₁ ispreferably not lower than 50%. When the working ratio P₂ is lower than5%, the work hardening of the raw material is insufficient so that theraw material cannot have satisfactory rigidity. The working ratio P₂mentioned herein can be derived from the following Expression (ii), inwhich A₁ designates a sectional area of the primary processed materialand A₂ designates a sectional area of the raw material (secondaryprocessed material) subjected to swaging.

Working Ratio P ₂(%)={(A ₁ −A ₂)/A ₁}×100   (ii)

The core wire subjected to the two processes of the wire drawing and theswaging is formed to have a wire diameter not larger than 0.5 mm and aYoung's modulus not lower than 50 GPa. As shown in FIG. 1, in the corewire 15 according to this embodiment, any other portion than the taperedfront end portion has a wire diameter D₂ not larger than 0.5 mm. Whenthe wire diameter of the core wire is larger than 0.5 mm, the core wirecan be used for the aorta etc., but it is difficult to use the core wirefor coronary intervention (PTCA), a peripheral system, etc. A practicalwire diameter applied to PTCA or a peripheral system in an existingguide wire is 0.24 to 0.34 mm.

The core wire having a wire diameter not larger than 0.5 mm is made tohave a Young's modulus not lower than 50 GPa. The Young's modulusmentioned herein shows a value when the strain of the core wire is 2%.That is, this core wire has high rigidity to be not lower than 50 GPa inspite of the fine wire diameter not larger than 0.5 mm. When the Young'smodulus of the core wire is lower than 50 GPa, the core wire is apt tocome short of pushability or torque transmission characteristic which ishowever required when the core wire is inserted into the microscopicblood vessel such as a coronary artery or a cerebral artery. Thus, thecore wire having the Young's modulus lower than 50 GPa is not suitableas a core wire according to the invention. In addition, it is preferablethat the Young's modulus is higher.

In this manner, the core wire in this embodiment is subjected to the twoprocesses of wire drawing and swaging, so that the working ratio of thecore wire can be improved as compared with the case where the core wireis subjected to the wire drawing alone or the case where the core wireis subjected to the swaging alone. Thus, the core wire can attain highrigidity to be not lower than 50 GPa in Young's modulus in spite of afine wire diameter not larger than 0.5 mm.

In addition, the texture of this core wire has a microcrystallinestructure because the two processes of wire drawing and swaging areperformed on the core wire. This will be described with reference toFIGS. 9A and 9B (the case where wire drawing is performed alone) andFIGS. 10A and 10B (the case where swaging is performed alone). In thecase where wire drawing is performed alone as shown in FIG. 9B and thecase where swaging is performed alone as shown in FIG. 10B, an image ofunclear rings whose outlines are intermittent is observed in an electrondiffraction pattern of each core wire. This electron diffraction patternis an image peculiar to an amorphous structure (so-called halo pattern).In the case where wire drawing is performed alone and the case whereswaging is performed alone, the texture of each core wire has anamorphous structure, as is also confirmed with reference to pictures oftextures shown in FIGS. 9A and 10A.

On the other hand, an electron diffraction pattern of a core wireaccording to the invention is obtained by using and imaging one and thesame sample as electron diffraction at two places. As a result, as shownin FIGS. 7B and 8B, an image of clear rings can be observed in theelectron diffraction pattern. Thus, the core wire has a microcrystallinestructure, as is also confirmed clearly with reference to pictures ofthe textures shown in FIGS. 7A and 8A.

In this manner, the textures of the core wire change from a metastableamorphous structure to a stable microcrystalline structure respectivelydue to both the wire drawing and the swaging performed on the core wire.Thus, the working degree (for example, hardness) increases, andmechanical characteristics such as tensile strength are improved.

The core wire in this embodiment is further subjected to heat treatmentso that strain, bending or residual stress caused by processing can beeliminated. For example, the heat treatment can be carried out on thecore wire at a temperature of 200 to 400° C. for 1 to 60 minutes whilethe core wire is retained in a certain shape.

Next, a method for manufacturing a core wire for guide wire according tothe invention will be described with reference to FIGS. 2A to 2C. Theaforementioned core wire for guide wire can be manufactured by thismethod for manufacturing a core wire for guide wire (hereinafterreferred to as “manufacturing method”).

This manufacturing method includes a primary process for drawing a rawmaterial M₀ into a primary processed material M₁ and a secondary processfor swaging the primary processed material M₁ into a secondary processedmaterial M₂ after the primary process, so as to manufacture a core wirewhich has a wire diameter not larger than 0.5 mm and a Young's modulusnot lower than 50 GPa.

First, as shown in FIG. 2A, the raw material M₀ having a wire diameterD₀ and made of a Ti—Ni based alloy is inserted into a hole 2 formed in awire-drawing dice 1 and extruded from the hole 2, or the raw material M₀is drawn out through the hole 2 of the wire-drawing dice 1. Thus, asshown in FIG. 2B, wire drawing is performed on the raw material M₀ so asto draw the raw material M₀ into a certain length while reducing thediameter of the raw material M₀. As a result, the primary processedmaterial M₁ having a wire diameter D₁ is shaped.

The inner diameter of the hole 2 of the wire drawing dice 1 is set sothat a working ratio P₁ when the raw material M₀ is drawn is madepreferably not lower than 10%, more preferably not lower than 20%, andmost preferably not lower than 30%.

Next, swaging is performed on the primary processed material M₁. Anapparatus used for the swaging in this embodiment has a pair of swagingdices 5 and 5 as shown in FIG. 2C. The pair of swaging dices 5 and 5 areformed to rotate in certain directions around the primary processedmaterial M₁ while colliding with and separating from the primaryprocessed material M₁ repeatedly. In addition, the swaging dices 5 and 5move sliding forward and backward along an axial direction of theprimary processed material M₁.

Then, the primary processed material M₁ is rotated in a certaindirection, and the pair of swaging dices 5 and 5 hammer and draw theprimary processed material M₁ while rotating on the periphery of theprimary processed material M₁ in a certain direction. At the same time,the same swaging dices 5 move over a certain range in the axialdirection of the primary processed material M₁. Thus, a secondaryprocessed material M₂ having a wire diameter D₂ not larger than 0.5 mmis shaped. In this embodiment, an unnecessary portion of the secondaryprocessed material M₂ is then further cut off, and a front end portionof the secondary processed material M₂ is processed into a tapered shapewith a reduced diameter. Thus, the core wire 15 having the wire diameterD₂ not larger than 0.5 mm as shown in FIG. 1 is manufactured. Thesecondary processed material M₂ may be used as the core material 15 asit is.

It is also preferable that the size of an arc-like recess formed in afront end portion of each swaging dice is set so that a working ratio P₂when the primary processed material is swaged can be made not lower than5%. Further, it is preferable that setting is done so that a totalworking ratio (P₁+P₂) of the working ratio P₁ and the working ratio P₂can be made not lower than 50%.

According to this manufacturing method, the two processes of wiredrawing and swaging are performed so that the working ratio of the corewire is improved, as compared with the case where wire drawing isperformed alone or the case where swaging is performed alone. As aresult, the hardness increase caused by work hardening becomes larger.And, it is possible to obtain a core wire which has high rigidity to benot lower than 50 GPa in Young's modulus while having the fine wirediameter not larger than 0.5 mm and which is prevented from fatiguedeformation.

Preferably, in this manufacturing method, heat treatment is performed onthe core wire after the aforementioned swaging. For example, the heattreatment is performed on the core wire 15 such that the core wire 15 iskept at a temperature 200° C. to 400° C. for 1 to 60 minutes. Sincestrain, bending, and residual stress caused by the wire drawing and theswaging are eliminated from the core wire 15 through the heat treatment,it is possible to obtain a core wire which has rigidity and is preventedfrom fatigue deformation and which has high linearity (not bending butkeeping a straight posture in its initial shape).

The core wire according to the invention manufactured by theaforementioned manufacturing method has the following operation andeffect.

That is, due to the two processes of wire drawing and swaging performedon the core wire according to the invention, the working ratio of thecore wire is improved as compared with the case where wire drawing isperformed alone or the case where swaging is performed alone. Thus, thehardness increase caused by work hardening becomes larger than in thecase where one of the aforementioned processings is performed alone.Therefore, the core wire according to the invention can attain highrigidity to be not lower than 50 GPa in Young's modulus while having thefine wire diameter not larger than 0.5 mm.

Since the core wire according to the invention has high rigidity whilehaving the fine wire diameter, the core wire is high in pushabilitywhich is required when the core wire is inserted into a tubular organand in toque transmission characteristic which is requested forselection of a blood vessel, and the core wire can be prevented fromfatigue deformation. Thus, for example, the core wire according to theinvention can be used suitably for guide wire to be inserted into anarrow blood vessel of a heart, a brain, etc.

In the background art, a raw material is drawn and then cut or ground soas to obtain a core wire for guide wire with a narrow size. However, thecost may be increased due to a large waste of the material because thedrawn raw material is cut. Further, the hardness and the rigidity may below because a work-hardened layer produced in the surface of the rawmaterial by the wire drawing is cut.

On the other hand, the wire diameter of the core wire is made not largerthan 0.5 mm by the swaging in which the raw material is hammered anddrawn. Thus, the yield of the material can be improved to reduce thecost, as compared with the case where the raw material is cut into acertain size. Further, since the swaging is performed after the wiredrawing in this embodiment, a work-hardened layer produced by the wiredrawing can be prevented from being cut, but the work hardening isfurther advanced. Thus, a core wire having high rigidity to be not lowerthan 50 GPa in Young's modulus can be obtained.

EXAMPLES

Mechanical characteristics, textures and hardness of various corematerials were evaluated.

(Prerequisite) Composition of Ti—Ni Based Alloy

Examples and Comparative Examples which will be described below weremanufactured using an alloy of Ti-51Ni (at %).

(1) Manufacturing of Comparative Examples and Examples ComparativeExample 1

A linear raw material was cut out from a Ti—Ni based alloy having theaforementioned composition, and wire drawing was performed on the rawmaterial. Thus, Comparative Example 1 was manufactured. The wirediameter was 0.475 mm, and the working ratio rate was 55%.

Comparative Example 2

A certain length of the raw material was cut out from ComparativeExample 1, and heat treatment was applied to the raw material such thatthe raw material was kept at 200° C. for 30 minutes. Thus, ComparativeExample 2 was manufactured. The working ratio was the same as that ofComparative Example 1, and the wire diameter was 0.478 mm (The wirediameter varies depending on oxides during the heat treatment. It isalso the same in Comparative Example 3 and Examples 2 and 3).

Comparative Example 3

A certain length of the raw material was cut out from ComparativeExample 1, and heat treatment was applied to the raw material such thatthe raw material was kept at 300° C. for 30 minutes. Thus, ComparativeExample 2 was manufactured. The working ratio was the same as that ofComparative Example 1, and the wire diameter was 0.482 mm.

Comparative Example 4

A linear raw material was cutout from a Ti—Ni based alloy having theaforementioned composition, and swaging was performed on the rawmaterial. Thus, Comparative Example 4 was manufactured. The wirediameter was 0.360 mm, and the working ratio was 98.9%.

Comparative Example 5

A certain length of the raw material was cutout from Comparative Example4, and heat treatment was applied to the raw material such that the rawmaterial was kept at 200° C. for 30 minutes. Thus, Comparative Example 5was manufactured. The working ratio and the wire diameter were the sameas those of Comparative Example 4.

Comparative Example 6

A certain length of the raw material was cut out from ComparativeExample 4, and heat treatment was applied to the raw material such thatthe raw material was kept at 300° C. for 30 minutes. Thus, ComparativeExample 6 was manufactured. The working ratio and the wire diameter werethe same as those of Comparative Example 4.

Comparative Example 7

In the same manner as Comparative Example 1, a linear raw material wascut out from a Ti—Ni based alloy having the aforementioned composition,and wire drawing was performed on the raw material. Thus, ComparativeExample 7 was manufactured. The wire diameter was 0.602 mm, and theworking ratio was 43.8%.

Example 1

A certain length of the raw material was cut out from ComparativeExample 1, and swaging was performed on the raw material. Thus, Example1 was manufactured. The wire diameter was 0.423 mm and the working ratioafter the swaging was 64%.

Example 2

A certain length of the raw material was cut out from Example 1, andheat treatment was applied to the raw material such that the rawmaterial was kept at 200° C. for 30 minutes. Thus, Example 2 wasmanufactured. The working ratio was the same as that of Example 1 andthe wire diameter was 0.416 mm.

Example 3

A certain length of the raw material was cut out from Example 1, andheat treatment was applied to the raw material such that the rawmaterial was kept at 300° C. for 30 minutes. Thus, Example 3 wasmanufactured. The working ratio was the same as that of Example 1 andthe wire diameter was 0.420 mm.

Example 4

A certain length of the raw material was cut out from ComparativeExample 7, and swaging was performed on the raw material with threeswaging dices. Thus, Example 4 was manufactured. The wire diameter was0.486 mm and the working ratio after the swaging was 64%.

Example 5

A certain length of the raw material was cut out from ComparativeExample 7, and swaging was performed on the raw material with twoswaging dices. Thus, Example 5 was manufactured. The wire diameter was0.512 mm and the working ratio after the swaging was 59%.

(2) Evaluation of Mechanical Characteristics

(a) Test Method

Each of Comparative Examples 1 to 7 and Examples 1 to 5 was processed sothat a test piece with a gauge length of 50 mm was manufactured. Each ofthese test pieces was set in a Tensilon tensile tester to repeat a cycle(load application, load removal, load application, . . . ) of applying atensile load to the test piece at a room temperature and with a testspeed of 1 mm/min so as to produce an elongation strain in the testpiece, and then removing the tensile load from the test piece. Therelation between tensile stress (MPa) and strain (%) was measured ineach test piece. The results are shown in FIGS. 3 to 6 and in Table 1.The Young's modulus on this occasion was calculated from the tensilestress at the strain of 2%.

In addition, Comparative Examples 1 to 3 are provided for examininginfluence of heat treatment on materials subjected to wire drawing (seeFIG. 3), and Comparative Examples 4 to 6 are provided for examininginfluence of heat treatment on materials subjected to swaging (see FIG.4). On the other hand, Examples 1 to 3 are provided for examininginfluence of heat treatment on materials subjected to both wire drawingand swaging (see FIG. 5), and Examples 4 and 5 are provided forexamining influence of kind of swaging (two dices or three dices) onmaterials subjected to swaging (see FIG. 6).

TABLE 1 Wire Drawing Swaging Wire Young's Working Working Heat DiameterModulus Target Drawing Sample Ratio (%) Ratio (%) Treatment (mm) (GPa)Note Influence of Heat Treatment FIG. 3 CE1 55 — — 0.475 49.2 — onMaterials Subjected to CE2 ″ — 200° C. × 30 min 0.478 43.8 heattreatment on sample Wire Drawing obtained from CE1 CE3 ″ — 300° C. × 30min 0.482 32.6 heat treatment on sample obtained from CE1 Influence ofHeat Treatment FIG. 4 CE4 —  98.9 — 0.360 58.9 — on Materials Subjectedto CE5 — ″ 200° C. × 30 min ″ 58.2 heat treatment on sample Swagingobtained from CE4 CE6 — ″ 300° C. × 30 min ″ 49.6 heat treatment onsample obtained from CE4 influence of Heat Treatment FIG. 5 Ex1 55 64 —0.423 63.4 wire drawing and swaging on on Materials Subjected to sampleobtained from CE1 Wire Drawing and Swaging Ex2 ″ ″ 200° C. × 30 min0.416 70.2 heat treatment on sample obtained from Ex1 Ex3 ″ ″ 300° C. ×30 min 0.420 60.5 heat treatment on sample obtained from Ex1 Influenceof Kind of Swaging FIG. 6 CE7  43.8 — — 0.602 40.7 same conditions asCE1 (with Three Dices or Two (different sample) Dices) on Materials Ex4″ 64 — 0.486 60.9 3-dice swaging on sample Subjected to Wire Drawingobtained from CE7 Ex5 ″ 59 — 0.512 60.7 2-dice swaging on sampleobtained from CE7 (CE = Comparative Example) (Ex = Example)

(b) Discussion of Test Results

As shown in FIG. 3, it is understood that the Young's modulus is reducedwhen heat treatment is performed after wire drawing (ComparativeExamples 2 and 3). The higher the temperature of the heat treatment is,the more conspicuous that tendency is. The same tendency is confirmed inthe case where heat treatment is performed after swaging as shown inFIG. 4.

FIG. 5 shows a stress-strain diagram of Examples 1 to 3. As isunderstood from the result of Example 1, the material subjected to thetwo processes of wire drawing and swaging has a high rigidity of 63.4GPa in Young's modulus in spite of a fine wire diameter of 0.423 mm.

In Comparative Examples shown in FIGS. 3 and 4, heat treatment leaded toreduction in Young's modulus. On the other hand, there was obtained aresult in Example 2 shown in FIG. 5 that the Young's modulus wasimproved in spite of heat treatment performed. That is, obtained was thefinding that the Young's modulus was improved by heat treatment on thematerial subjected to the two processes of wire drawing and swagingwhile the Young's module was reduced by heat treatment on the materialsubjected to wire drawing or swaging only. This is because the metaltexture has a microcrystalline structure due to the combination of wiredrawing and swaging. That is, heat treatment performed after wiredrawing or heat treatment performed after swaging leads to loss inenergy (reduction in Young's modulus) due to recrystallization, whileheat treatment performed after wire drawing and swaging leads to no lossin energy (no reduction in Young's modulus).

FIG. 6 shows Young's modulus in the case where swaging was performedwith three dices (Example 4) and Young's modulus in the case whereswaging was performed with two dices (Example 5). The number of diceshad little influence, but it could be confirmed that the Young's moduluswas improved in each case.

(3) Evaluation of Textures

Textures and electron diffraction patterns of Comparative Examples 1 and4 and Example 1 were observed with a transmission electron microscope(TEM). The results are shown in FIGS. 7A to 8B (Example 1), FIGS. 9A and9B (Comparative Example 1) and FIGS. 10A and 10B (Comparative Example4). Incidentally, Example 1 was observed in two different positions(FIGS. 7A to 8B).

As shown in FIGS. 9B and 10B, the electron diffraction patterns ofComparative Examples 1 and 4 have unclear images peculiar to anamorphous structure. Also from FIGS. 9A and 10A, it is understood thatstructures in Comparative Examples 1 and 4 are amorphous.

On the other hand, as shown in FIGS. 7B and 8B, the electron diffractionpattern of Example 1 has a clear ring-like image peculiar to acrystalline structure. Further as shown in FIGS. 7A and 8B, it is alsounderstood from the texture pictures that the texture of Example 1 has amicrocrystalline structure. Thus, the two processes of wire drawing andswaging lead to a microcrystalline structure in the texture.

(4) Evaluation of Hardness

Vickers hardness (Hv) was measured in Comparative Examples 1 and 4 andExample 1 whose textures were observed in (3). Vickers hardness wasmeasured outside the texture and inside the texture in each sample witha load of 200 kg. The results are shown in FIG. 11.

As shown in FIG. 11, the Vickers hardness in Comparative Example 1subjected to wire drawing only is comparatively low, and the Vickershardness in Comparative Example 2 subjected to swaging only iscomparatively high but varies widely. On the other hand, in Example 1subjected to wire drawing and swaging, the Vickers hardness is high bothinside the texture and outside the texture, and low in variation. It istherefore understood that the texture structure of Example 1 is highlystable.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   10 guide wire-   15 core wire for guide wire (core wire)

1. A core wire for guide wire, wherein the core wire is made of a Ti—Nibased alloy, has a wire diameter not larger than 0.5 mm and has aYoung's modulus not lower than 50 GPa, and wherein wire drawing andswaging are performed on the core wire.
 2. (canceled)
 3. The core wireof claim 1, wherein the Ti—Ni based alloy is a work-hardened Ti—Ni basedalloy whose texture has a microcrystalline structure.
 4. The core wireof claim 1, wherein heat treatment as well as the wire drawing and theswaging is performed on the core wire.
 5. A method for manufacturing thecore wire of claim 1, the method comprising: drawing a raw material madeof a Ti—Ni based alloy, and then carrying out swaging to obtain a corewire having a wire diameter not larger than 0.5 mm and a Young's modulusnot lower than 50 GPa.
 6. The method of claim 4, further comprising:performing heat treatment after the swaging.